It is well known that gases such as air can be dissolved into and carried by liquids such as water. For example, it is common to find dissolved air in deionized water supply lines in chemical and biological research facilities, clinical chemistry laboratories and hospitals. It is also common to find gas bubbles in such water supply lines.
Although many uses of such deionized water supplies may tolerate dissolved gas as gas bubbles very well, such gas in some applications can prove troubling. As an example, the performance of automated clinical chemistry analyzers can be adversely affected by the gas often found in deionized water supply lines.
More particularly, it is common practice in automated clinical chemistry analyzers to employ a sample transfer system to transfer samples, such as patient body fluid specimens, from a sample cup to a reaction cuvette. In the reaction cuvette, reagents may be added to the sample and the resulting reaction monitored to ultimately determine the concentration of a substance in the sample. Typically, the sample transfer system includes a probe that is connected both to a precision metering syringe-type pump and to a source of deionized water. The probe may be connected via a flexible tube or conduit to a tee fitting with the tee fitting in turn connected to the syringe pump and to a pinch valve that is supplied with deionized water. The syringe pump is used to draw a precise predetermined volume of sample into the probe and then dispense the sample volume into the reaction cuvette. Once such a transfer is completed, the pinch valve is opened and deionized water is passed through the probe to flush the interior of the probe. The external surfaces of the probe may also be washed to thereby minimize carryover of sample from one transfer operation to the next.
A common problem experienced with sample transfer systems like the one just described is the formation or collection of gas bubbles in the conduit between the syringe pump and the probe. Deionized water remains in this portion of the conduit after the probe has been flushed. In part because the retained deionized water is no longer under pressure and due to cooling of the conduit, dissolved gas in the water comes out of solution, forming gas bubbles in the conduit. Also, gas bubbles in the deionized water supply may find their way into this portion of the conduit. Unfortunately, the amount of sample metered by the syringe pump may vary due to the compressibility of these gas bubbles. These variations can be particularly troubling because the accuracy of the sample analysis depends in part upon the precision with which the sample is metered into the reaction cuvette.
Automated analyzers of the type just described also commonly employ reagent transfer systems for transferring reagents from storage vessels to the reaction cuvette. Such reagent transfer systems may be essentially identical to the sample transfer system just described and thus suffer from the same difficulty with the accuracy of reagent volume delivered to the reaction cuvette. Also, reagents may be stored in a refrigerated environment. Before being transferred to the reaction cuvette, the reagents must be heated to the reaction temperature. This heating is also known to cause dissolved gasses in the reagents to form gas bubbles either in the reagent transfer system or in the reaction cuvette where such bubbles can interfere with the sensing technique, such as electrochemistry, colorimetry, or nephelometry.
Thus, it is known in clinical chemistry analyzers to attempt to remove gas from liquids before gas bubbles can form or collect which may affect analyzer performance. For example, it is known to utilize a degasser in the form of a small liquid reservoir having an open end over which a membrane or a hydrophobic filter is retained. The membrane or filter is permeable to gas but is not permeable to liquid. With the passage of time, dissolved gas or gas bubbles in the liquid held in the reservoir will gradually pass through the gas permeable membrane or filter. Unfortunately, this type of liquid degasser is very slow and can only be used where very small volumes of liquid are required over a given time period. If the membrane fails or if the hydrophobic filter becomes wetted, liquid leakage from the reservoir will result. Also, if a large gas bubble or a series of smaller bubbles enter the reservoir, the bubbles may be drawn through the degasser before the gas bubbles can pass through the membrane or filter.
Thus, there is a need for a liquid degassing system which can quickly process larger volumes of liquid than those devices known in the prior art. Furthermore, such a system should reduce or eliminate potential leakage which may otherwise result from membrane failure in such known systems.